Reviewing the Latest Findings on the Polypeptide Sequence of the SARS-CoV-2 S-Protein to Raise Questions about the Origins of RaTG13

The ongoing coronavirus disease outbreak started from a local seafood market of the Wuhan city (China). The first reported infections were six seafood street-sellers with severe pneumonia admitted to the intensive care unit of the Wuhan Jin-Yin-Tan Hospital. Upon metagenomics sequencing and phylogenetic analysis of the complete genomes of the virus isolates from these patients, RaTG13, a bat coronavirus previously detected in Rhinolophus affinis from the Chinese province of Yunnan, was identified as the most identical and closely-related coronavirus to the human pathogen, which was designated as SARS-CoV-2. The most updated evidences suggest adaptation of the human coronavirus SARS-CoV-2 from an animal reservoir, which supposedly underwent some sort of recombination. However, the processes to describe how adaptation of the virus from an animal to a human host may occur still cannot be explained. From a polypeptide sequence analysis of the S-proteins of SARS-coronaviruses, this contribution address questions about the origins of RaTG13, which still remains the most identical strain with SARS-CoV-2 described up to now.